The present invention relates generally to the field of intravascular medical devices for stent delivery. More specifically, the present invention relates to an intravascular stent delivery catheter that provides medial balloon inflation for deterring longitudinal displacement of a stent during deployment.
Balloon dilation catheters have been, and continue to be, a popular means of stent delivery. Current balloon catheters, however, are prone to difficulties when attempting to accurately deploy the stent across a stenosed lesion. Accurate deployment of the stent is important to the clinician, as he or she wants to place the stent directly on the diseased tissue of the vessel. Should the stent migrate to either side of the diseased tissue, some of the diseased tissue may be left untreated. In addition, healthy tissue may be adversely affected by the inaccuracy of the stent deployment procedure.
Stent misplacements occur because of specific inflation dynamics experienced by the expandable balloon when deploying the stent. Currently existing stent delivery catheters inflate the balloon portion of the catheter preferentially from either the distal or proximal end of the balloon. During inflation, the expanding balloon may form an inflation xe2x80x9cwavexe2x80x9d that may be said to drive or xe2x80x9cplowxe2x80x9d the stent so that it opens progressively from one end to the other along the front of the inflation wave. This form of balloon inflation is referred to as xe2x80x9cend-to endxe2x80x9d preferential inflation. End-to-end balloon inflation causes a deploying stent to displace longitudinally away from its intended delivery site, thereby potentially ineffectively treating the diseased lesion within the patient""s vasculature.
In addition to end-to end preferential inflation, preferential balloon inflation may also arise from the initial inflation of the proximal and distal ends of the balloon, wherein the inflation from both ends progresses medially. This form of preferential balloon inflation is referred to as xe2x80x9cdog boning.xe2x80x9d In some cases, such as with rigid stents, this balloon inflation dynamic may be a preferred means of limiting stent migration. With more flexible stents, however, the dog bone balloon inflation dynamic may cause the ends of the stent to shorten with respect to one another. As the proximal end and the distal end of the stent are expanded, the ends are driven toward one another. In effect, the length of the stent is forced to compress due to this particular balloon inflation dynamic.
For many applications, it is desirable to have a stent delivery catheter comprising an inflation balloon that inflates evenly. For other applications, it would additionally be desirable to provide a stent delivery catheter having a balloon that incorporates preferential inflation of a beneficial type, such as initial medial inflation.
While inadvertent preferential expansion is to be avoided, some controlled preferential balloon inflations are actually desired. With initial medial inflation, for example, the expandable balloon inflates initially at its center, with inflation then progressing simultaneously towards both ends of the balloon. The center of the balloon is initially maximally inflated, causing the center of the expanding stent to impinge upon the center of the treatable lesion or stenosis. This initial medial impingement greatly reduces longitudinal displacement of the stent during its further expansion. The balloon and stent are then allowed to expand evenly toward their respective ends resulting in securing of the stent over its length in the diseased vessel.
Medial balloon inflation is difficult to predict and achieve with currently available expandable balloons. The physics behind fluid dynamics dictates that fluid will always take the path of least resistance when filling open space. Thus, a balloon will inflate where the fluid or inflation media gathers first. From this point, a bolus of fluid will move tangentially across the balloon filling it as it moves. This inflation phenomenon is synonymous with the end-to-end balloon inflation dynamic. Similarly, two boluses of fluid may aggregate at the confining ends of the balloon and fill medially. This inflation phenomenon is synonymous with the dog bone balloon inflation dynamic.
The present invention provides a balloon where the inflation dynamics are optimized (preferably from the center outward), thereby providing for the homogeneous expansion of both the expandable balloon and stent. In an alternate embodiment of the present invention, an expandable balloon is provided that incorporates a plurality of inflatable members that may be individually controlled to achieve predictable medial balloon inflation.
To prevent dog-bone type or end-to-end preferential inflation, and provide instead either no preferential inflation or, in an alternate embodiment, medial inflation, the present invention provides a means for directing and restraining entering inflation fluid within the distensible balloon. In a representative embodiment of the invention, a medially positioned inflation member captures an initial bolus of inflation fluid entering the balloon. This inflation member serves as a dam to gather a bolus of inflation fluid while creating a space for the fluid to fill. In one embodiment, this inflation member is rupturable. Once the member bursts, the unrestrained inflation fluid is released into the remaining portions of the expandable balloon. The expandable balloon is then further inflated to expand the remaining portions of both the balloon and stent.
In an alternative embodiment of the present invention, the inflation member does not rupture. The inflation member of this embodiment is comprised of a semi-permeable material. The material forming the inflation member selectively leaks at sufficiently high pressures. Thus, the bolus of fluid restrained within the inflation member slowly leaches from the inflation member, thereby expanding the remaining portions of both the balloon and stent.
In another embodiment of the present invention, a wire member is disposed over the distal end of the stent delivery catheter. The wire member expands and contracts with the longitudinal displacement of tubular members within the catheter""s shaft. With the appropriate displacement of the tubular members, the wire member first medially expands, impinging the center of a loaded stent against the diseased lesion. In particular embodiments, an expandable balloon may be disposed over the wire member. The expandable balloon may then be inflated to further expand the remaining portions of both the balloon and stent.